PROJECT SUMMARY/ABSTRACT The financial burden of medications is a significant barrier to medication adherence and subsequent diabetes control. Benefit designs that reduce copayments for services that are seen to be more cost-effective (known as ?value-based insurance designs? or VBIDs) continue to capture the attention of public and private insurers, employers, and policy makers as a strategy to improve adherence and reduce long-term costs. While VBID programs that reduce copayments for chronic illness medications have been shown to have a positive short- term impact on medication adherence, we know less about long-term sustainability of clinical gains over time, particularly when incentives are eliminated. Also, little is known about which factors affect who participates and who benefits when VBID programs are introduced by a health plan in a real-world, multi-employer setting. This study will evaluate the provision and discontinuation of a real-world VBID program called the WellRx Drug Rider -- a zero copay drug benefit offered to engage patients more effectively in their self-care. To take advantage of this unique natural experiment, we will use a multi-method approach including patient- mailed surveys, semi-structured interviews of patients, providers, and employers, and a quasi-experimental longitudinal study using pre-post with comparison group and patient-level interrupted time series with comparison series to evaluate the impact of WellRx among patients with diabetes. This study is motivated by four specific aims: (1) to examine determinants of decisions about WellRx participation among employers and patients with diabetes and assess differences in at-risk patient subgroups (e.g., race and socioeconomic status); (2) to examine changes in self-management, utilization and costs, and clinical outcomes (HbA1c, lipid, blood pressure control) over a 1-year baseline and up to 4-year follow-up, comparing patients whose employers offered the free program compared to propensity-matched patients whose employers did not; (3) to assess sustainability of outcomes following program discontinuation, comparing patients whose employers continue or choose to discontinue WellRx coverage in later follow-up years; and (4) to determine whether the changes observed in Aims 2 and 3 differ by race/ethnicity, income, education attainment, or baseline nonadherence. The proposed study addresses pragmatic questions in a real-world health system that is highly motivated to improve access to care, self-efficacy, and outcomes for a diverse population of patients with diabetes. Our findings will inform future efforts to create benefit designs that are provider-endorsed, align with patient needs, address barriers to patient engagement, and improve patient capacity to maintain effective diabetes control.